The present invention relates to blends of polymers, particularly blends of polyolefins.
The use of certain transition metal compounds to polymerise 1-olefins, for example, ethylene, is well established. The use of Ziegler-Natta catalysts, for example, those catalysts produced by activating titanium halides with organometallic compounds such as triethylaluminium, is fundamental to many commercial processes for manufacturing polyolefins. Over the last twenty or thirty years, advances in the technology have led to the development of Ziegler-Natta catalysts which have such high activities that olefin polymers and copolymers containing very low concentrations of residual catalyst can be produced directly in commercial polymerisation processes. The quantities of residual catalyst remaining in the produced polymer are so small as to render unnecessary their separation and removal for most commercial applications. Such processes can be operated by polymerising the monomers in the gas phase, or in solution or in suspension in a liquid hydrocarbon diluent. Polymerisation of the monomers can be carried out in the gas phase (the xe2x80x9cgas phase processxe2x80x9d), for example by fluidising under polymerisation conditions a bed comprising the target polyolefin powder and particles of the desired catalyst using a fluidising gas stream comprising the gaseous monomer. In the so-called xe2x80x9csolution processxe2x80x9d the (co)polymersation is conducted by introducing the monomer into a solution or suspension of the catalyst in a liquid hydrocarbon diluent under conditions of temperature and pressure such that the produced polyolefin forms as a solution in the hydrocarbon diluent. In the xe2x80x9cslurry processxe2x80x9d the temperature, pressure and choice of diluent are such that the produced polymer forms as a suspension in the liquid hydrocarbon diluent. These processes are generally operated at relatively low pressures (for example 10-50 bar) and low temperature (for example 50 to 150xc2x0 C.). Commodity polyethylenes are commercially produced in a variety of different types and grades. Homopolymerisation of ethylene with transition metal based catalysts leads to the production of so-called xe2x80x9chigh densityxe2x80x9d grades of polyethylene. These polymers have relatively high stiffness and are useful for making articles where inherent rigidity is required. Copolymerisation of ethylene with higher 1-olefins (e.g., butene, hexene or octene) is employed commercially to provide a wide variety of copolymers differing in density and in other important physical properties. Particularly important copolymers made by copolymerising ethylene with higher 1-olefins using transition metal based catalysts are the copolymers having a density in the range of 0.91 to 0.93. These copolymers which are generally referred to in the art as xe2x80x9clinear low density polyethylenexe2x80x9d are in many respects similar to the so called xe2x80x9clow densityxe2x80x9d polyethylene produced by the high pressure free radical catalysed polymerisation of ethylene. Such polymers and copolymers are used extensively in the manufacture of flexible blown film.
WO 99/12981 discloses that ethylene may be polymerised by contacting it with certain Fe, Co, Mn or Ru complexes of selected 2,6-pyridinecarboxyaldehydebis(imines) and 2,6-diacylpyridinebis(imines); and WO 99/46302 discloses catalysts comprising a mixture of complexes such as those disclosed in WO 99/12981 and other known catalysts for the polymerisation of 1-olefins, such as Phillips (chromium) catalysts, Zeigler catalysts or metallocenes.
We have discovered that blending two or more polymers, one of which has been made using a catalyst such as the above-mentioned iron catalyst, and another of which has been made using a different catalyst, can result in polymers whose properties are synergisticxe2x80x94ie are more than merely additive.
Thus the present invention provides a 1-olefin polymer comprising a blend of
(1) one or more polymers made using a late transition metal catalyst, and
(2) one or more polyolefins made using a free radical process or polymerised using a Phillips type (chromium oxide) catalyst, a metallocene catalyst, or a Ziegler-Natta catalyst.